Abstract

Manganese doped nanocrystalline willemite powder phosphors $Zn_{2-x}Mn_xSiO_4$ $(0.1 \leq x \leq 0.5)$ have been synthesized by a low-temperature initiated, self-propagating, gas producing solution combustion process. The phosphors have been characterized by using x-ray diffraction (XRD), energy dispersive spectroscopy, scanning electron microscopy, Fourier transform infrared spectroscopy (FTIR), electron paramagnetic resonance (EPR), and photo luminescence (PL) spectroscopic techniques. The lattice parameters calculated from XRD confirm that Zn2–xMnxSiO4 has a rhombohedral space group R3H. The XRD patterns confirm that $Zn_{2-x}Mn_xSiO_4$ phosphor samples undergo a phase transformation from \beta -willemite to \alpha -willemite phase at 950 °C. The EPR spectra of Mn2+ ions exhibit resonance signals at g \cong 3.24 and g \cong 2.02, with a sextet hyperfine structure centered around g \cong 2.02. The EPR signals of Mn2+ give a clear indication of the presence of two different Mn2+ sites. The magnitude of the hyperfine splitting (A) indicates that the Mn2+ is in an ionic environment. The number of spins participating in resonance (N), the paramagnetic susceptibility (\chi ), and the zero-field splitting parameter (D) have been evaluated as function of x. It is interesting to observe that the variation of N with temperature obeys Boltzmann. The paramagnetic susceptibility is calculated from the EPR data at various temperatures and the Curie constant and Curie paramagnetic temperature was evaluated from the 1/ \chi versus T graph. The luminescence of Mn2+ ion in Zn2SiO4 shows a strong green emission peak around 520 nm from the synthesized phosphor particles under UV excitation (251 nm). The luminescence is assigned to a transition from the upper 4T1 6A1 ground state. The mechanism involved in the generation of a green emission has been explained in detail. The effect of Mn content on luminescence has also been studied.